Asda and Sainsbury's cannot attempt another merger for at least 10 years, the Competition and Markets Authority has confirmed.
Formally closing its investigation into the proposed tie up, it said the supermarket giants were legally bound not to join forces for a decade, which is the standard CMA prohibition period.
The ban also applies to US giant Walmart, which is not allowed to acquire any interest in Sainsbury's as long as it still owns part of Asda.
The CMA blocked the tie-up in April over fears it would raise prices for consumers. The deal would have created the UK's biggest supermarket chain, accounting for £1 in every £3 spent on groceries.